1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of achieving an enhancement in aperture ratio, and an enhancement in picture quality reliability.
2. Discussion of the Related Art
Generally, there are liquid crystal display (LCD) devices of various modes according to various alignments of liquid crystal molecules. For example, LCD devices are classified into a twisted nematic mode, in which liquid crystal directors are controlled by a vertical electric field, and an in-plane switching mode, in which liquid crystal directors are controlled by a horizontal electric field.
The in-plane switching mode LCD device includes a color filter array substrate, a thin film array substrate arranged to face the color filter array substrate, and a liquid crystal layer interposed between the color filter array substrate and the thin film array substrate. The color filter array substrate includes a black matrix for preventing leakage of light, and color filter layers formed on the black matrix, to render a desired color. The thin film transistor array substrate includes gate lines and data lines defining unit pixels, thin film transistors formed at respective intersections of the gate lines and data lines, and common electrodes and pixel electrodes formed in parallel, to form a horizontal electric field.
In order to secure a desired capacitance of each storage capacitor, the in-plane switching mode LCD device has a structure in which a common line, which is formed such that it is connected with the common electrode in each pixel region, is overlapped with the pixel electrode in the pixel region under the condition in which an insulating film is interposed between the common line and the pixel electrode. In this case, a reduction in aperture ratio occurs due to the common lines arranged over and beneath each pixel region. Since the common lines are formed using the same metal layer as that of the gate lines, there may be a short circuit between the common electrodes and the gate lines. In order to prevent a failure caused by a short circuit between the common electrodes and the gate lines, a sufficient spacing distance should be secured between the common electrodes and the gate lines. For this reason, a reduction in aperture ratio occurs.
As the LCD device has a larger area, the length of the common lines also increases. As a result, the resistance of the common lines, which is proportional to the length of the common lines, is also increased. In this case, there may be a phenomenon that the common voltage is distorted or delayed. When the area of the common lines is increased to solve this problem, a reduction in aperture ratio occurs. Furthermore, a parasitic capacitor is formed between the gate line and the common line in each sub-pixel. This parasitic capacitor causes cross-talk, a flicker phenomenon, image sticking, etc.